Jetting the Carburetors on a Yamaha V-Star 1100.

Jetting the Carburetors on a Yamaha V-Star 1100.
--By Steve Schneider
CycleForay
Copyright 2004
All content, images, etc. is the intellectual property of Steve Schneider and protected by United States and International
Copyright laws. Copying, plagiarizing, or using the content to create related artwork is prohibited without the written
permission from Steve Schneider.
If you have input to provide to the guide, please do not hesitate to contact Steve Schneider. Upon each revision, a
contributor’s list will be updated to reflect the name of those who have contributed to the content of the guide.
Revision Level: 1
Contributors: Steve Schneider (Author), Larry,
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From the Author:
This guide has been compiled so that a person can make an educated decision before deciding
to jet his or her own carburetors. I hope that it acts as a tool for encouragement. The process
is a simple one but a delicate one. If you can hold a baby, you can jet your own carburetors.
Whatever air kit you decide to purchase or if you are jetting the carburetors because of a new
exhaust system, you should read this guide before spending money having a mechanic perform
the jetting process. You will, at the very least, understand what is involved and what the
mechanics are going to be doing to your motorcycle. You may be the type of person that only
trusts their bike to a trained mechanic… this is fine… think of this guide as educational only.
But, if you are the type who likes to work on their own bike… use this guide as a tool to allow
you to perform the operation without confusion. I hope that you find this guide informative and,
more importantly, accurate. If you do find any errors, I would like to correct them. Please email
questions or comments to [email protected]. Thanks and enjoy the guide.
Use disclaimer:
This comprehensive guide will attempt to cover all aspects of performing a complete rejetting of
the V-Star 1100’s carburetor system. If you decide to move forward and perform your own
rejetting, you do so at your own risk. Portions of this guide describe removing, disassembling,
and even drilling your stock carburetors. One slip could be the difference between a successful
rejetting and a trip to the dealer to order new carburetors. Just promise me that you won’t hold
me responsible for your own mishaps. Thanks… shall we move on? Yes.
Prologue:
When thinking about rejetting the carburetors on your V-Star 1100, I think about it as a 2-stage
process with many intermediate steps. The first stage is getting the carburetors off the bike.
The second stage is performing the actual rejetting. This comprehensive guide will walk you
through the process step by step. First we will discuss removing the carburetors and every step
involved and second we will cover the rejetting process. The turning of every screw will be
addressed. When you have read this entire guide, you will be ready to perform the rejetting
process. Once finished, you will be proud of yourself. A new understanding of how the
motorcycle breathes, will give you the confidence to try just about anything pertaining to the
maintenance of your 1100. If you will gather up the following tools on the tool list… we can get
started.
Tool List:
3mm Allen wrench
5mm Allen wrench
10mm wrench or socket
12mm wrench or socket
#2 Philips head screwdriver
Flat tipped screwdriver
Pliers
Needle nosed vise grips
Battery powered drill
Drill bit
Small flat tipped screwdriver
Others…
If you are savvy enough to stop reading here… this is a quick list that shows the basic
chronology of the process.
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Remove air filter housing
Remove the seat or seats
Disconnect Fuel Lines (also the vapor line from tank to charcoal canister on California models)
Disconnect instrument connectors from the fuel tank
Remove fuel tank
Remove air box
Disconnect TPS and heater connectors
Remove chrome carb cover
Disconnect Fuel Lines
Remove rubber carb elbows
Disconnect throttle cables from carbs
Remove the carbs
Perform the jetting
1. Remove the Chrome air filter housing.
To remove the chrome dog-dish (air filter housing) from the right side of the bike, you will need
to remove the two mounting bolts and loosen the clamp that holds the air duct to the back of the
housing. You will need a 5 mm Allen wrench and a #2 Philips screwdriver.
2. Remove the seats.
This can be accomplished by using a 5 mm Allen wrench and removing the Allen head bolt from
just behind the rear seat and the bolt just behind the front seat. Pulling up and back will free the
seats. One smooth motion will do it.
3. Gain access to the dashboard plug and unplug it (It is white)
Note: Your trip odometer will lose its count, please record the number if you wish to save your
current mileage for this tank of gas.
Figure A shows the three plastic rivets that need to be removed to gain access to the dashboard
plug. Using your Philips head screwdriver, press the small circle in the middle of the rivets
down… a click is felt. Remove the rivets by hand. You have freed the cover and you may lift it
up to expose the electrical connector that needs to be unplugged. Figure B shows the plug.
FIGURE A
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FIGURE B
4. Remove the gas tank
Refer back to Figure A to see the two bolts that hold the gas tank to the frame. These can
be removed with your 12 mm wrench or socket. Now you must remove the fuel line from the
selector switch on the left side of the tank. Figure C shows the selector switch and the fuel
supply hose. Turn the selector to the OFF position and use your pliers to relocate the hose
clamp. With a container in hand to catch the fuel, remove the hose from the selector switch.
A small amount of fuel will need to be collected from the hose. Now you can remove the
fuel tank by placing one hand on the bracket that held the tank down and the other on the
front of the tank… pull up gently and back and forth… the tank will come off to the rear of
the bike. Be careful not to hit the triple tree or the risers. Tank removal is best performed
while low on fuel. Place the tank somewhere to prevent accidental damage.
FIGURE C
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5. Remove the air-box
In order to remove the airbox, first remove the duct that connected the air filter housing to the
air-box. This can be done by loosening the clamp that holds the duct to the air-box. A Philips
head screwdriver is used to accomplish this. Once the duct is removed, the air box can be
removed by removing the bolt. This bolt is located at the rear of the airbox. A 10 mm wrench or
socket is used here. Before lifting the airbox up and off, you will need to loosen the clamps that
hold the airbox to the rubber carburetor elbows. A #2 Philips screwdriver is used here. The
clamps are under the airbox and they are accessed one on either side of the bike. Now lift off
the box and remove the breather hose from the bottom of the airbox. The airbox is now free…
please set it aside.
Note: You may notice oil… motor oil… everywhere! Just wipe it away with a clean rag. Having
the crankcase slightly over-filled with oil usually causes the presence of oil here. Check the level
if you feel you have excessive oil residue. This is nothing to worry about.
6. Disconnect the choke and throttle cables from the carburetor assembly.
Before removing the cables you will need to unbolt the chrome cover that hangs on the left side
of the bike. This is the decorative carburetor cover. To remove this cover use your 3 mm Allen
wrench. Refer back to Figure C if you have trouble locating the cover. The V-Star 1100 has
one choke cable and two throttle cables. Figure D shows the screw that holds the choke cable.
Loosen this screw with you Philips screwdriver, and then the cable can be released by actuating
the choke linkage, shown red in Figure D, by hand and sliding the cable end out through the
bottom of the choke cam. The throttle cables are removed from the carburetors by using your
10 mm wrench. Figure E shows the nuts that need to be loosened to remove the cables. The
cable A as shown in Figure E can be removed by loosening the bottom nut and then pulling the
cable up and over the mounting bracket. Slide the cable end out of the throttle cam. Cable B,
as shown in Figure E, can be removed by loosening the tall nut on the top of the bracket and
then removing the cable end from the throttle cam. Reinstallation of cable A may require you to
slacken the cable at the throttle end of the cable.
FIGURE D
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FIGURE E
7. Remove the rubber intake elbows from the carburetors
Using your Philips screwdriver, loosen the clamps on the carburetor side of the elbow ducts and
remove them from the carburetors. Wipe any oil out of them and set them aside. Figures F and
G show the elbows.
FIGURE F
FIGURE G
8. Remove the fuel lines
There is a fuel line on each carburetor that needs to be removed. You will need your small
container to catch any fuel that may come out of the hoses once they are removed. The fuel
lines are highlighted in Figure F and Figure G. Your pliers will be used here to relocate the hose
clamps.
9. Unplug the carburetor heaters and the TPS (throttle position sensor)
Figure H shows the two plugs that need to be unplugged before removing the carburetors.
There is a small tang near the tappet cover that needs to be bent a little to free the wiring so the
carburetors can be removed. We are getting close to removing the carbs… take a break.
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FIGURE H
10. Remove the carburetors
You are now ready to remove the carburetors from the motorcycle. It is necessary to loosen the
clamps that hold the carburetors to the intake boots. You will need your 3 mm Allen wrench to
perform this operation. Once you have the clamps loose, you can take hold and remove the
carbs. The carburetors will be removed from the left of the motorcycle. To remove the
carburetors from the boots, take them with both of your hands and turn the whole assembly
counter-clockwise while rotating the carburetor in your right hand up and the carburetor in your
left hand down. You will be able to see how both carburetors will be freed from the intake boots
simultaneously. Once you have them free, maneuver them out to the left of the motorcycle. A
small amount of fuel may leak out because the bowls are still full. You may put rags over your
gearbox to absorb any dripped fuel. You may drain the bowls before removing the carburetors,
but we find that not much fuel leaks out and it is easier to drain them while on the bench. Once
you have the carburetors out, try to keep them level so that no fuel leaks out. Figures I and J
show the carburetors before and after removal.
FIGURE I
FIGURE J
11. Drain the fuel from the carburetor bowls
Figure K shows the carburetor assembly after it has been removed from the motorcycle. Figure
L identifies the carburetor drain screws. The float bowls will need to be drained, one at a time,
into a small container… such as an empty coffee can. It is easier to grasp the screws with a
needle nosed vise grip rather than a Philips screwdriver due to the fact that the screws are soft
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and they will damage easily. So, grasp the drain screw and turn it counter-clockwise to loosen
it. Once you get it started, you can continue to loosen it with your Philips screwdriver until the
fuel begins to drain. While holding the carburetors over the container, the fuel will begin to flow
from the bottom of the carburetor. Repeat this for both carburetors.
Figure K
FIGURE L
Prologue to the actual jetting process
Now that you have the carburetor out and drained. Place them on the bench while keeping
them upright. You may have to prop them up somehow. Use your imagination here. We need
to discuss the process before we go inside the carburetors.
There are many reasons that you may want to rejet your carburetors, but the only jets we will be
concerning ourselves with are the pilot jets, the main jets, the metering needles, and the PMS
(pilot mixture screw). The V-Star 1100 comes from the factory equipped with Mikuni
carburetors. They are jetted as follows… again speaking only about the jets mentioned.
Front cylinder carburetor:
• 112.5 Main Jet
• 17.5 Pilot Jet
• (1) 0.020” thick shim washer under the needle
• PMS setting apparently varies from bike to bike… but it should be 2.5 turns
Rear cylinder carburetor:
• 110 Main Jet
• 17.5 Pilot Jet
• (1) 0.020” thick shim washer under the needle
• PMS setting apparently varies from bike to bike… but it should be 2.5 turns
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You probably noticed that the front cylinder is equipped with a larger main jet than the rear.
This is the way the 1100’s are set up from the factory and it is not a mistake. Depending on
what you are doing, your choice of jet sizes may vary. If you have simply added slip-on mufflers
to improve the sound of your V-Star, you probably don’t need to rejet. If you have added a full
exhaust system, you can probably get away with putting a 115 main in the front carburetor and
moving your 112.5 main jet from the front carburetor to the rear carburetor. Then you can turn
your PMS out to 3 turns. To adjust the PMS you simply turn it all the way in and back it out the
prescribed number of turns. The location of the jets will be covered shortly. Another reason to
rejet your carburetors would be if you were installing an “air kit”. These kits, available from
various manufacturers, are designed to allow the intake of your motorcycle to breathe easier.
This results in more airflow, which results in more power. Flow becomes a major factor here
and all of the various air-kits should come with the recommended jets to make the required
changes to the carburetors. Instructions should also be included, which means that this article
can act as a supplemental resource while you are performing the work. The jets inside the
carburetor all perform certain roles in the fuel delivery process, but it all boils down to the throttle
range that the motorcycle is operating at. The PMS screw simply allows you to adjust the
mixture for efficiency while idling. The pilot jet is a low range jet, where the main jets work in
conjunction with the metering needles to keep the mixture optimal at the mid to high range and
at wide open throttle. The needles meter the fuel through the main jets by moving up and down
with the diaphragm that resides under the black covers on the top of the carburetors. There is
also a throttle valve connected to the diaphragm. We won’t get any more technical than this
right now. Lets talk about performing the actual work. Here we go…and remember… do not
separate the two carburetors during this procedure.
12. Accessing the needles
The needles are accessed by removing the top covers from the carburetors. Needle
adjustments should be performed one carburetor at a time. Figure M shows the covers.
Note: Needle adjustments can be performed while the carburetors remain installed on the
motorcycle, but for the purpose of this guide, we have removed the carburetors.
Each cover has two Philips screws that need to be removed. Once removed, lift the cover
slowly because there is a large spring under there. Set the cover aside and remove the spring.
Figure N shows the cover off and the spring. Now, gently loosen the rubber diaphragm around
the edges so that the throttle valve can be removed from the carburetor. Figure O shows the
throttle valve assembly. You must now get the needle out by pulling out the white needle
retainer. Figure P shows the needle retainer as installed in the throttle valve. Using a needle
nose pliers, you can pull up while twisting to gently remove the retainer. It is just, sort of, a snap
fit. BE CAREFUL HERE! There is a small spring under the retainer. You may want to perform
this operation with the throttle valve inside a plastic bag. This way, if the spring goes flying, it
will be contained in the bag. Figure Q shows the needle retainer and spring as removed from
the throttle valve. You may get lucky and have the spring remain intact on the retainer. Once
you have this out, set the retainer and the spring aside and get ready to remove the needle.
The needle is removed from the top. Place your finger inside the throttle valve and cover the
needle hole. Now you can turn the throttle valve upside down and carefully remove the needle.
Figure R shows the anatomy of the needle.
Note: The needle in Figure R has two, additional shim washers present because the motorcycle
used to take photographs is equipped with an air-kit that required these.
If you are installing an aftermarket needle, follow the manufacturers instructions pertaining to how
to configure it before reassembly. If you are simply shimming the stock needle, the shims go over
the tip of the needle to raise it up when assembled. Installation of the needle is the reverse.
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FIGURE M
FIGURE N
FIGURE O
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FIGURE P
FIGURE Q
FIGURE R
You have now successfully shimmed the needles or replaced them. Reinstall them into the
carburetors and put the covers back on. When reinstalling the throttle valve assembly, be sure
to get the edge of the diaphragm down evenly and put the cover on carefully. A mistake here
may cause the motorcycle to run badly. We will be moving on the main jets and the pilot jets
next.
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13. Remove the float bowl
This is probably going to be the most frustrating portion of the entire process. It will be difficult
to remove the float bowl screws without damaging them. If your kit didn’t come with any, I
suggest that you purchase some. The best choice would be a stainless steel Allen head cap
screw… M4-.7 pitch, 10 mm long. You will need (8) of these total. Don’t forget to get (8) lock
washers too. Using your needle nose vise grips, break free the four screws that hold the bowl
on. Once free, you can use your Philips screwdriver to remove them completely. Take off the
carburetor bowl and set it aside. Figure S shows the bottom of the carburetor. Figure T shows
the arrangement of the jets.
FIGURE S:
This carburetor has been jetted before, therefore, the
float bowl screws do not look like the ones supplied
from the factory. Also, you may notice that the
carburetor heater is broken.
FIGURE T
This carburetor is equipped
with an aftermarket PMS screw
that has incorporated a thumb
adjustment, so it will not look
like your stock carburetor.
14. Remove and replace the main jets and the pilot jets
Refer to Figure T, unscrew the appropriate jets and replace them. Installation is reverse of
removal. Only the small, top portion of the main jet needs to be removed. A flat tipped
screwdriver can be used to accomplish this. You have now rejetted and are ready to put
everything back together.
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FIGURE U
15. Drill out the PMS plug, if equipped, and adjust the idle screw
Once you have installed the jets and have the carburetors back together, you must drill out the
PMS plug so that you may make your idle circuit adjustments. There are two plugs visible on
the bottom of the carburetor. Figure U shows the location of the PMS plug. The correct plug to
drill out is the one that sits higher and that has the little hole in it. It is directly between the
carburetor heater and the big Philips screw. NOTE: THE CARB IN THE PICTURE SHOWS AN
AFTERMARKET PMS SCREW… SO DO NOT DRILL THE PLUG THAT IS RECESSED. This
operation is, by far, the most delicate procedure of the entire job. For best results, a batterypowered drill that stops immediately upon releasing the trigger is required. The plug is about a
¼ inch thick so it may feel like you are drilling deep, but if you go slowly you will be OK. Make
small, short runs and be sure not to hit the PMS screw hiding below the plug. Once you have
the plug drilled out you will be able to see the PMS screw. This can be adjusted with a narrow
flat tipped screwdriver. To adjust it… turn it all the way in (clockwise)… and them turn it out the
prescribed number of turns. The number of turns will vary depending on what your air kit setup
is like.
16. Initial startup
You have completed everything now and are ready to start the bike, huh. Well, if you have
followed all the instructions it should start right up. You will hear the fuel pump ticking as it
pressurizes and fills the float bowls up. Before you do any extensive riding… you should
synchronize the carburetors… although… the bike will normally run fine, it is still recommended
to perform this additional operation. Carburetor synchronization will not be covered here.
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Additional tips and photos…
This photo shows the PMS screws (top left),
the pilot jets (top right), the main jets
(bottom left) and the M3, 0.020” thick brass
shim washers (bottom right)
Part numbers for the jets are as follows…
Mikuni Main Jets: KN102.221-110 the last
number is the size
Mikuni Pilot Jets: KVM28/486-17.5 again, the
last number is the size.
Also, do not separate the two carburetors during this procedure.
Contributor tips:
• When drilling out the PMS plugs, you can make a drill stop by slipping a piece of 1/4"
copper tubing over the drill bit so only a 1/4" of the length of the drill is exposed. (Larry)
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